st.metrics can be a string: in this case it shouldn't show the arrow up/down:

st.metrics("label", value=20, delta="Going up") is rendered as ↑ Going up

Currently the down arrow is shown when the string begins with minus, but the minus itself is not removed from the visualized text:
st.metrics("label", value=10, delta="Going down") is rendered as ↑ Going down
st.metrics("label", value=10, delta="-Going down") is rendered as ↓ -Going down

It would be more intuitive to remove the arrow in case of a string parameter, and left to the user to add it to the string just in case of need. This change would also allow to use the delta text as an extra field to add additional info not strictly related to value changes such as in:

st.metrics("label", value=10, delta="Value is nominal").

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